Design and fabrication of silicon-based high-NA metalenses for microscopic imaging

To address the demand for on-chip integrated optical components in the 1310 nm communication band, this work designs and fabricates a high-numerical-aperture (high-NA) geometric-phase metalens based on a complementary metal oxide semiconductor (CMOS)-compatible single-crystal silicon platform. The device employs geometrically optimized elliptical silicon nanopillars for phase modulation based on the geometric phase principle. Simulation results show that the metalens achieves near-diffraction-limited focusing with a simulated focusing efficiency of 23.3% and an NA of 0.95. Experimentally, the fabricated device realizes high-NA focusing with a measured efficiency of 13.2% and a focal spot full width at half maximum (FWHM) of 1.954 μm. For the first time at this wavelength and under such a high NA, a systematic comparison between simulation and experiment quantitatively reveals the pronounced sensitivity of the metalens performance to nanofabrication errors, thereby providing key data for process-tolerance design. Furthermore, the metalens successfully demonstrates clear imaging of a target with a linewidth of 49.6 μm, verifying its basic functionality and potential for integrated photonic systems. This study not only presents a complete demonstration from device design through fabrication and testing but also, via in-depth simulation-experiment analysis, fills the research gap in the systematic investigation of fabrication-error effects on high-NA geometric-phase metalenses at the important 1310 nm wavelength, thereby offering important empirical insights and optimization directions toward the practical deployment of such devices.